Recently, small-sized computers such as mini computers and personal computers have been widely employed, and hence it has become very important to store computer data with high security. Magnetic recording tapes which are named "back-up tapes" have been employed for this purpose. The magnetic recording tapes must have not only great storage capacity but also high running endurance. Further, it is also needed for the magnetic recording tapes to store the data without failure even under severe environmental conditions (for example, drastic variations of temperature and/or humidity).
The back-up tape generally comprises a non-magnetic flexible plastic web (i.e., support) and a magnetic recording layer provided thereon. In order to increase recording density (data storage capacity per unit area), a non-magnetic layer and a thin magnetic layer may be provided on the non-magnetic support web in order.
The magnetic recording layer preferably has a smooth surface in consideration of electromagnetic characteristics, but the smooth surface sometimes causes troubles such as wrong tape winding and jerky running. For obviating these troubles, a back-coating layer is generally provided on the back surface of the support web, that is, on the surface of the support opposite to the surface on which the magnetic recording layer is provided.
Japanese Patent Provisional Publication No. H5(1993)-182178 discloses a magnetic recording tape in which a non-magnetic layer and a thin magnetic layer are provided on one surface of a non-magnetic support web in order, and a back-coating layer is provided on the other surface. As material for the non-magnetic support web, the publication suggests aromatic polyamide such as aramide.
Japanese Patent provisional Publication No. H9(1997)-115134 proposes a magnetic recording tape having an improved back-coating layer provided on the back surface of the support web. The improved back-coating layer comprises a binder and particles dispersed therein, and the particles are two kinds of carbon black (which have mean particle size differing from each other), a calcium carbonate powder having a specific particle size, and other inorganic material powders having a specific particle size and a Mohs' scale of hardness of 5 to 9. According to the publication, the back-coating layer gives high running endurance to the magnetic recording tape, and hence the proposed tape is very suitable for storing computer data.
The back-up tapes have been getting thinner to increase storage capacity, and accordingly a support web of the tape has been needed to have a higher rigidity. As material for the rigid support web, aromatic polyamide (i.e., aramide) is considered to be suitable. The present inventors, however, have noted that a back-coating layer shows unsatisfactory adhesion to the aromatic polyamide support web, and consequently that various troubles are liable to occur while the recording tape is repeatedly run in contact with a magnetic head and guide pins of recording/reproducing device. For example, the edge of the recording tape is often damaged upon repeated contact with the magnetic head and/or the guide pins, and further wastes coming from damaged recording tape sometimes increase friction of the tape.
Accordingly, it is an object of the present invention to provide a magnetic recording medium in which a back-coating layer adheres well to an aromatic polyamide support so that the damage of edge of the tape is obviated if the tape repeatedly runs in recording/reproducing devices. The magnetic recording medium of the invention is preferably employed as a magnetic recording tape for computer data storage.